As we discussed, changing the message signature here breaks repairs when there are mixed-clusters (eg. during an upgrade/downgrade). This is because [xfer/3](https://github.com/basho/riak_core/blob/7fc16113303b28b606eb68f07775e7c4a64247b6/src/riak_core_handoff_manager.erl#L107) does a direct cross-node cast that uses the signature from the old code. Could potentially fix by supporting a shim match here that just calls the other, but likely not worth it for 1.4.0.